1. Field of the Invention
The present invention relates to a silicon carbide semiconductor device and to a process for manufacturing same, and, for example, it relates to high-power vertical-insulating gate-type field effect transistors.
2. Description of the Related Art
In recent years there have been proposed vertical power MOSFETs fabricated using silicon carbide monocrystal materials as the power transistors. Such devices have trenches from the substrate surface to the semiconductor substrate, with the sides of the trenches acting as the channel regions. Power transistors require a low leak current between source and drain during gate voltage off times and a low resistance between source and drain during on times (hereunder referred to as "on resistance") and, in order to meet these requirements, power transistors which make use of the advantageous electronic properties of hexagonal silicon carbide to provide effective reduction in lead current during application of high voltage and reduction in on resistance are described, for example, in Japanese Unexamined Patent Publication No. 7-131016 and Japanese Unexamined Patent Publication No. 7-326755.
However, the trench gate-type power MOSFETs described in Japanese Unexamined Patent Publication No. 7-131016 and No. 7-326755 do not necessarily provide improved channel mobility, and still have a problem of high on resistance. Another problem has been the short life of the gate insulating films compared to those in silicon MOSFETs.
It is therefore an object of the present invention to provide a transistor which is a vertical insulating gate-type field effect transistor made of silicon carbide and having a highly reliable gate insulating film, as well as a process for its manufacture, and also to provide a transistor which allows improved channel mobility and an effective reduction of on time resistance, as well as a process for its manufacture.